In the post operative treatment of patients, it is usually desirable to supply oxygen or oxygen enriched air to a patient for a period of say 5 to 15 minutes to assist in reoxygenating the patient to offset the effects of the anaesthetic. Usually oxygen is available in recovery rooms from suppliers which are capable of delivering oxygen at a rate of about 4 to 6 liters per minute. Unfortunately this is less than the rate of inspiration of a typical adult patient. Some attempts have been made to provide an oxygen storage device which can store oxygen from a relatively low capacity supply so as to be able to deliver the oxygen or oxygen enriched air to the patient at a relatively high rate during inspiration.